1. Field of the Invention
This invention relates to a highly repetitively pulsed laser device with a laser resonator which forms "go" and "return" paths for a light pulse.
2. Description of Related Art
Examples of a highly repetitively pulsed laser device are an active mode-locked laser device in which an acousto-optical (AO) element inserted in a laser resonator is modulated with a frequency f.sub.0 =c/(2L), where L is the laser resonator length equal to the mode interval so that a high-speed light pulse having a short time width is produced, and a passive mode-locked device in which a saturable absorber dye solution is inserted in the laser resonator so that a high-speed light pulse having a short time width is produced. In the above-described active mode-locked laser device, reflection of a high frequency electrical signal for modulation of the AO element with an ultrasonic wave is monitored, and electrical control is so performed that the reflection of the high frequency electrical signal is stabilized and the light pulse output is stabilized. On the other hand, in the above-described passive mode-locked laser device, the concentration of the saturable absorber dye solution and the magnitude of the exciting energy are so controlled that the light pulse output is stabilized.
However, the active mode-locked laser device suffers from a difficulty that to achieve stabilization of the light pulse output, the electrical control for stabilization of the strength of the ultrasonic wave applied to the AO element is rather intricate.
The passive mode-locked laser device is disadvantageous in that, in the stabilization of the output light pulse, it is difficult to adjust the magnitude of the exciting energy with respect to the concentration of the saturable absorber dye solution because, in association with the deterioration of the dye, adjustment of the concentration of the saturable absorber dye solution is difficult.